The doctor is in

Marc Rowe found this information and it's related to a tennis stroke but certainly applies to any motion.

Technique: The Kinetic Chain
10/12/04 6:57 PM
(The information in this article was taken or adapted from the High
Performance Coaching Program Study Guide.)
The parts of the body act as a system of chain links, whereby the
energy or force generated by one link (or part of the body) can be
transferred successively to the next link. The link system in the service
action, which starts from the ground, can be explained in the following way
(Elliott and Saviano, 2001; Elliott & Kilderry, 1983):
a.. Leg drive
b.. Trunk rotation
c.. Upper arm elevation
d.. Forearm extension, upper arm internal rotation and forearm
pronation
e.. Hand flexion
The optimum coordination (timing) of these body segments and their
movements will allow for the efficient transfer of energy and power up
through the body, moving from one body segment to the next. Each movement
in the sequence builds upon the previous motion and they all contribute to
the generations of racket speed.
This transfer of energy in sequential coordination is also enhanced by
the stretch-shortening cycle of muscle action. The stretch-shortening cycle
involves the active stretching (the muscle is activated but is elongated by
another force) of a muscle in a countermovement immediately followed by a
more forceful shortening of the muscle in the desired direction. In the
forehand, for example, the chest and shoulder muscles are actively stretched
(coaches often use the cue "loading" here) as the trunk rotates into the
shot and the inertia of the arm and racket cause them to lag behind.
The active stretch of the muscle stores energy in the elastic elements
of muscle and associated tissues such as tendons, which is reused as the
muscle begins to shorten. This sequence of muscular coordination tends to be
chosen naturally by the brain, but sometimes this must be coached in players
who develop pauses, that in turn lead to missed segment rotations or
problems in sequencing segments.
The most effective tennis strokes begin with leg drive generating
ground reaction forces that can be transferred up the segments of the
kinetic chain to the racket. Proper timing of the segments in the kinematic
chain and stretch-shortening cycle muscle actions maximize the transfer of
energy to generate the greatest racket speed.
Example-One-handed backhands tend typically involve five kinematic
links that the player has to coordinate (Groppel, 1992). In most cases the
one-handed backhand is based on a sequential summing of the motions of the
legs, trunk, arm, forearm, and wrist/hand. Two-handed backhands during
early learning use fewer body segments, so many young players find this
stroke easier to coordinate. In the modern two-handed stroke a similar
number of segments are rotated as for the on-handed stroke.